Package and method for integration of heterogeneous integrated circuits

ABSTRACT

In some embodiments, the present disclosure relates to a package for holding a plurality of integrated circuits. The package includes a first conductive pad disposed over a first substrate and a second conductive pad disposed over a second substrate. The second conductive pad is a multi-layer structure having an uppermost metal layer including titanium or nickel. A molding structure surrounds the first substrate and the second substrate. A conductive structure is over the first substrate and the second substrate. The conductive structure is conductively coupled to the second conductive pad.

REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No. 15/855,305, filed on Dec. 27, 2017, which is a Continuation of U.S. application Ser. No. 15/223,609, filed on Jul. 29, 2016 (now U.S. Pat. No. 9,865,481, issued on Jan. 9, 2018), which is a Divisional of U.S. application Ser. No. 14/015,513, filed on Aug. 30, 2013 (now U.S. Pat. No. 9,419,156, issued on Aug. 16, 2016). The contents of the above-referenced Patent Applications are hereby incorporated by reference in their entirety.

BACKGROUND

Optical signals are usable for data transmission between optical devices. Optical signal transmitters and/or receivers are often fabricated in one type of integrated circuit (IC) chip, such as those using semiconductor substrates primarily made of class III-V semiconductor compound, while signal processor ICs controlling the optical signal transmitters and/or receivers often employ a second type of IC chip, such as those using semiconductor substrates primarily made of silicon (Si). Devices, such as optical devices, employing heterogeneous ICs of different types are useful. However, conductive connection between different types of ICs in a conventional multi-chip module often employs either wire bonding or flip-chip bonding. For wire bonding, the conventional multi-chip module is large and signal speeds are limited. For flip-chip bonding used in a conventional multi-chip module, due to different contact pad metals such as gold (Au) or aluminum/copper (Al/Cu) pads, two different bump formation processes such as gold-gold (Au—Au), gold-tin (Au—Sn), and/or tin silver/silver tin copper (SnAg/SnAgCu) are used. These solder bump formation processes in flip-chip bonding add cost and reduce overall yield.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are illustrated by way of example, and not by limitation, in the figures of the accompanying drawings, wherein elements having the same reference numeral designations represent like elements throughout.

FIG. 1 is a cross-sectional view of a package in accordance with one or more embodiments.

FIG. 2 is a flow chart of a method of making a package in accordance with one or more embodiments.

FIGS. 3A-3D are cross-sectional views of a package at various stages of production in accordance with one or more embodiments.

FIGS. 4A-4B are cross-sectional views of structures for conductive contact in accordance with one or more embodiments.

DETAILED DESCRIPTION

It is understood that the following disclosure provides one or more different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, examples and are not intended to be limiting. In accordance with the standard practice in the industry, various features in the drawings are not drawn to scale and are used for illustration purposes only.

Moreover, spatially relative terms, for example, “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” “left,” “right,” etc. as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of the present disclosure of one features relationship to another feature. The spatially relative terms are intended to cover different orientations of the device including the features.

In some applications, a chip having an optical component (also referred to as an optical chip) is encapsulated by a molded package structure, and the molded package structure is mounted on a PCB substrate. Compared with a configuration without using the molded package structure, the embodiments described herein allow a shortened conductive path between the optical chip and the PCB. In some embodiments, shortened conductive path means lowered parasitic capacitance and resistance along the conductive path, and thus in turn helps to decrease power loss and increase operation frequency of the resulting device. In some embodiments using an interposer to connect the molded package structure and the PCB substrate, a through-silicon-via structure formed in the interposer is capable of being fabricated after mounting the molded package structure to the interposer (i.e., “via-last” process). By doing so, fabrication processes and masks for forming bump structures on corresponding sides of the interposer and the molded package structure are omitted.

FIG. 1 is a cross-sectional view of a package structure 100 in accordance with one or more embodiments. Package structure 100 includes a first chip 110, a second chip 120, a first passivation layer 130, a redistribution structure 140 over first passivation layer 130, and a second passivation layer 150 over redistribution structure 140. Package structure 100 further includes a molding structure 152 surrounding and underneath first chip 110 and second chip 120. In some embodiments, redistribution structure 140 connects multiple chips such as first chip 110 and second chip 120 in a fan-out process, i.e., a process having more chips receiving a particular signal than transmitting that signal such that the signal is “fanned-out”.

In some embodiments, first chip 110 includes one or more active components and/or passive components configured to process, receive and/or transmit electrical signals. Examples of passive components include, but are not limited to, resistors, capacitors, and inductors. Examples of active components include, but are not limited to, diodes, field effect transistors (FETs), metal-oxide-semiconductor FETs (MOSFETs), complementary metal-oxide-semiconductor (CMOS) transistors, and bipolar transistors. In some embodiments, first chip 110 includes a bare chip or die. In some embodiments, first chip 110 includes a stack of chips. In some embodiments, first chip 110 is configured to perform predetermined logic, analog, or mixed mode functionality. In some embodiments, first chip 110 has a thickness ranging from 50 micrometers (μm) to 750 μm.

First chip 110 includes at least one conductive pad 112 on an upper surface 114 of first chip 110. Conductive pad 112 is conductively coupled to the one or more active components and/or passive components of first chip 110 for communication of electrical signals between first chip 110 and external circuitry. Example materials of the conductive pad 112 include, but are not limited to, aluminum, copper, or a combination thereof. First chip 110 further has a passivation layer 116 over the upper surface 114. Passivation layer 116 has an opening that exposes at least a portion of conductive pad 112. Example materials of the passivation layer 116 include, but are not limited to, silicon oxide, silicon nitride, low dielectric constant (low-)k dielectric materials such as carbon doped oxides, extremely low-k dielectric materials such as porous carbon doped silicon dioxide, or a combination thereof.

Second chip 120 includes at least one optical component 122 configured to process, receive, and/or transmit optical signals. Second chip 120 is thus also referred to as an optical chip in some applications. Optical signals are electromagnetic signals capable of being shaped and are different from electrical signals which are signals carried by electrical charges, such as electrons, holes, or ions. In some embodiments, optical signals include electromagnetic signals having a wavelength of less than 1 millimeter (mm). Examples of optical components include, but are not limited to, light emitting devices such as lasers and light emitting diodes, light detecting devices such as photo-sensors, optical modulators, and optical couplers. In at least one embodiment, second chip 120 further includes one or more active and/or passive components configured to process, receive and/or transmit electrical signals converted to/from optical signals by the optical component 122. In some embodiments, second chip 110 has a thickness ranging from 150 μm to 350 μm.

Second chip 120 includes at least one conductive pad 124 on an upper surface 126 of first chip 120. Second chip 120 also has a passivation layer 128 over upper surface 126 and exposing a portion of conductive pad 124. Example materials of the conductive pad 124 include, but are not limited to, aluminum, copper, gold, or a combination thereof. Example materials of the passivation layer 128 include, but are not limited to, silicon oxide, silicon nitride, low-k dielectric materials such as carbon doped oxides, extremely low-k dielectric materials such as porous carbon doped silicon dioxide, or a combination thereof. In some embodiments, passivation layer 128 and passivation layers 130 and 150 have an optical opening 154 defined therein to allow transmitting and/or receiving of optical signals by the optical component 122. In at least one embodiment, passivation layer 128 is made of a material transparent to optical signals transmitted and/or received by the optical component 122, and a portion of the optical opening 154 corresponding to the passivation layer 128 is thus omitted. In some embodiments an optical waveguide and reflective surface are arranged to define an optical path from the optical component 122 of the first chip 120 through the optical opening 154 to the waveguide through the reflective surface.

Passivation layer 130 is over and covering conductive pads 112 and 124 and passivation layers 116 and 128. In some embodiments, passivation layer 130 includes epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), or other organic dielectric materials. In one or more embodiments, passivation layer 130 is formed of a material similar to the material used for forming passivation layers 116 or 128, such as silicon oxides, silicon nitrides, low-k dielectric materials, extremely low-k dielectric materials, or a combination thereof. In at least one embodiment, passivation layer 130 is made of a material transparent to optical signals transmitted and/or received by the optical component 122, and a portion of the optical opening 154 corresponding to the passivation layer 130 is thus omitted. In some embodiments, passivation layer 130 has a thickness ranging from 3 μm to 10 μm.

Redistribution structure 140 is conductive and includes a first conductive structure 142 conductively coupled to the conductive pad 112 and a second conductive structure 144 conductively coupled to the conductive pad 124. In the embodiment depicted in FIG. 1, first conductive structure 142 and second conductive structure 144 are connected and in physical contact at a reference line 146. First conductive structure 142 includes a planar portion 142 a substantially in parallel with upper surface 114 of first chip 110 and a protrusion 142 b connecting the conductive pad 112 and the planar portion 142 a. Second conductive structure 144 includes a planar portion 144 a substantially in parallel with upper surface 126 of second chip 120 and a protrusion 144 b connecting the conductive pad 124 and the planar portion 144 a. In the embodiment depicted in FIG. 1, planar portions 142 a and 144 b are in physical contact with each other at reference line 146. In some embodiments, planar portions 142 a and 144 b are not in physical contact with each other.

In some embodiments, conductive structures 142 and 144 include copper, aluminum, nickel, gold, tungsten, or a combination thereof. In some embodiments, conductive structures 142 and 144 each have one or more conductive layers suitable for obscuring metal atoms from diffusion into structures above or underneath redistribution structure 140. In some embodiments, conductive structures 142 and 144 are also referred to as post-passivation interconnect (PPI) structures. In some embodiments, conductive structures 142 and 144 are formed using a CMOS Back-End-of-Line (BEOL) process.

Second passivation layer 150 is over and covering redistribution structure 140. In some embodiments, passivation layer 150 includes epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), or other organic dielectric materials. In one or more embodiments, Second passivation layer 150 is formed of a material similar to the material used for forming the passivation layers 116 or 128, such as silicon oxides, silicon nitrides, low-k dielectric materials, extremely low-k dielectric materials, or a combination thereof. In some embodiments, passivation layer 150 and passivation layer 130 are made of different materials. In at least one embodiment, passivation layer 150 is made of a material transparent to optical signals transmitted and/or received by the optical component 122, and a portion of the optical opening 154 corresponding to the passivation layer 150 is thus omitted. In some embodiments, passivation layer 150 has a thickness ranging from 3 μm to 10 μm.

Molding structure 152 is surrounding and underneath first chip 110 and second chip 120 to protect surfaces of chips 110 and 120 that are not covered by passivation layers 130 and 150. In some embodiments, molding structure 152 has a thickness that is sufficient to enclose bottom surfaces of chips 110 and 120. In some embodiments, molding structure 152 comprises a material that has a thermal expansion coefficient about or between those of chips 110 and 120. In some embodiments, molding structure 152 comprises a material that has a thermal expansion coefficient ranging from 4 to 9. In some embodiments, example materials of the molding structure 152 include, but are not limited to silicone, including silicone rubber, resins, including epoxy resins, other resins, or other epoxy materials.

Although only one conductive pad 112 or 124 for each chip 110 or 120 and only two corresponding conductive structures 142 and 144 are depicted in FIG. 1, in some embodiments, there are more than one conductive pad on each chip 110 or 120 and are variously connected by redistribution structure 140. In some embodiments, there are one or more other chips in addition to chips 110 and 120 included in the package structure 100. In some embodiments, only one of first chip 110 and second chip 120 is present, and the other one of first chip 110 and second chip 120 is omitted.

FIG. 2 is a flow chart of a method of making a package in accordance with one or more embodiments. It is understood that additional processes are not precluded from being performed before, during, and/or after the method 200 depicted in FIG. 2.

In operation 260, tape is deposited onto a first support surface. The tape is a thermal tape for adhering to a first support surface on one side of the tape and adhering to a first chip and the second chip on another side of the tape. If the temperature of the tape is raised sufficiently high, the tape dissolves. In some embodiments, the tape is an ultraviolet (UV) optical tape. The first support surface is a polished, substantially planar, silicon substrate. In some embodiments, the first support surface is glass. In at least some embodiments, the use of glass reduces cost.

FIG. 3A is a cross-sectional view of a package 100 following operation 260 in accordance with one or more embodiments. Tape 182 is deposited onto a first support surface 180. First chip 110 and second chip 120 are illustrated above the tape 182 prior to contact with the tape.

Returning to FIG. 2, in operation 262, the first chip is deposited onto the tape. The first chip includes one or more active components and/or passive components configured to process, receive and/or transmit electrical signals.

In operation 264, the second chip is deposited onto the tape. The second chip includes at least one optical component configured to process, receive, and/or transmit optical signals. In some embodiments, the first chip and second chip are deposited together.

In operation 266, a molding structure is deposited over the first chip, the second chip and the tape. In some embodiments, the molding structure includes silicone. The molding structure covers the first chip, the second chip and the tape. The molding structure is deposited in a layer between about 50 μm and about 750 μm thick. If the molding structure is too thin, the first chip and second chip are not covered by the molding structure. If the molding structure is too thick, molding structure material is wasted. In some embodiments, the coefficient of thermal expansion is between that of the first chip and the second chip.

In operation 268, a second support surface deposited onto the molding structure. Similar to the first support surface, the second support surface is a polished, substantially planar, silicon substrate. In some embodiments, the first support surface is glass. In at least some embodiments, the use of glass reduces cost. The second support surface adheres to the molding structure. The second support surface functions as a carrier and as a heat sink for the first chip and the second chip.

FIG. 3B is a cross-sectional view of the package 100 following operations 262-268 in accordance with one or more embodiments. The first chip 110 and the second chip 120 are deposited onto the tape 182. Molding structure is deposited over the first chip 110, the second chip 120 and the tape 182. A second support surface 184 is deposited onto the molding structure.

Returning to FIG. 2, in operation 270, the tape and first support surface are removed and the package is rotated 180 degrees around an axis passing through FIG. 2 (flipped), as illustrated.

In operation 272, a first passivation layer is deposited over the package. In some embodiments, passivation layer 130 includes epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), or other organic dielectric materials.

FIG. 3C is a cross-sectional view of the package 100 following operations 270 and 272 in accordance with one or more embodiments. The tape 182 and the first support surface 180 are removed and the package 100 is flipped. A first passivation layer 130 is deposited over the package 100.

Returning to FIG. 2, in operation 274, the first passivation layer is etched by a photolithography process to expose a conductive pad on the first chip and a conductive pad on the second chip.

In operation 276, a redistribution structure is deposited onto the first passivation layer and the conductive pad on the first chip and the conductive pad on the second chip to conductively couple the conductive pads. In some embodiments, excess redistribution structure is removed by a photolithography process.

FIG. 3D is a cross-sectional view of the package 100 following operations 274 and 276 in accordance with one or more embodiments. The first passivation layer 130 is etched and the redistribution structure 140 is deposited onto the first passivation layer and the conductive pad 112 on the first chip 110 and the conductive pad 124 on the second chip 120 to conductively couple the conductive pads.

Returning to FIG. 2, in operation 278, a second passivation layer is deposited over the package. The second passivation layer is similar to the first passivation layer.

In operation 279, the passivation layers are etched by a photolithography process to create an optical opening to expose an optical component of the second chip. The second chip includes at least one optical component configured to process, receive, and/or transmit optical signals. FIG. 1 illustrates the package after operation 279 with the second planar surface 184 removed.

FIG. 4A is a cross-sectional view of a structure for conductive contact in accordance with one or more embodiments. A positively doped (p-type) contact layer 488, such as in the pad 124 of the second chip 120 (as illustrated in FIG. 1), has a first metal layer 489 over and in contact with the p-type contact layer, a second metal layer 490 over and in contact with the first metal layer, and a third metal layer 491 over and in contact with the second metal layer to form a p-type contact 400A. In some embodiments the first metal layer 488 includes titanium (Ti), the second metal layer 490 includes platinum (Pt) and the third metal layer 491 includes a titanium (Ti) nickel (Ni) alloy.

FIG. 4B is a cross-sectional view of a structure for conductive contact in accordance with one or more embodiments. A negatively doped (n-type) contact layer 492, such as in the pad 124 of the second chip 120 (as illustrated in FIG. 1), has a first metal layer 494 over and in contact with the n-type contact layer, a second metal layer 495 over and in contact with the first metal layer, a third metal layer 496 over and in contact with the second metal layer, and a fourth metal layer 498 over and in contact with the third metal layer to form an n-type contact 400B. In some embodiments the first metal layer 494 includes nickel (Ni), the second metal layer 495 includes a germanium (Ge) gold (Au) alloy, the third metal layer 496 includes nickel (Ni) and the fourth metal layer 498 includes a titanium (Ti) nickel (Ni) alloy.

One aspect of this description relates to a package for holding a plurality of heterogeneous integrated circuits. The package includes a first chip having a first conductive pad and a first substrate including a first semiconductor and a second chip having a second conductive pad and a second substrate including a second semiconductor, wherein the second semiconductor is different from the first semiconductor. The package also includes a molding structure, the first chip and the second chip embedded in the molding structure, a conductive structure over the first chip and conductively coupled to the first conductive pad and over the second chip and conductively coupled to the second conductive pad, and a passivation layer over the conductive structure, the passivation layer comprising an opening defined therein, the opening exposing a portion of the second chip.

Another aspect of this description relates to a package for holding a plurality of heterogeneous integrated circuits. The package includes a first chip having a first conductive pad and a first substrate including a first semiconductor and a second chip having a having a second conductive pad doped p-type, a third conductive pad doped n-type and a second substrate including a second semiconductor, wherein the second semiconductor is different from the first semiconductor. The second conductive pad includes a p-type contact on the second chip, a first metal layer over the p-type contact, a second metal layer over the first metal layer and a third metal layer over the second metal layer. The third conductive pad includes an n-type contact on the second chip, a fourth metal layer over the n-type contact, a fifth metal layer over the fourth metal layer, a sixth metal layer over the fifth metal layer and a seventh metal layer over the sixth metal layer. The package includes a molding structure, the first chip and the second chip embedded in the molding structure, a conductive structure over the first chip and conductively coupled to the first conductive pad and over the second chip and conductively coupled to the second conductive pad doped p-type or the third conductive pad doped n-type, and a passivation layer over the conductive structure, the passivation layer comprising an optical opening defined therein, the opening exposing an optical component of the second chip.

Yet another aspect of this description relates to a method of integrating heterogeneous integrated circuits. The method includes depositing tape onto a first support surface, depositing a first chip onto the tape, wherein the first chip has a first conductive pad and a first substrate including a first semiconductor, depositing a second chip onto the tape, wherein the second chip has a second conductive pad and a second substrate including a second semiconductor, wherein the second semiconductor is different from the first semiconductor, depositing a molding structure over the first chip, second chip and the tape, depositing a second support surface onto the molding structure, removing the tape and first support surface, depositing first passivation layer, etching first passivation layer, depositing a conductive structure to conductively couple the first pad and the second pad, and depositing a second passivation layer over the first passivation layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A package for holding a plurality of integrated chips, comprising: a first conductive pad disposed over a first substrate; a second conductive pad disposed over a second substrate, wherein the second conductive pad is a multi-layer structure having an uppermost metal layer comprising titanium or nickel and an underlying metal layer comprising a same material as the uppermost metal layer; a molding structure surrounding the first substrate and the second substrate; a conductive structure over the first substrate and the second substrate, the conductive structure conductively coupled to the first conductive pad and the second conductive pad; a first passivation layer having a first segment disposed over the first substrate and a separate second segment disposed over the second substrate, wherein the first segment has a first outer sidewall that is separated from a second outer sidewall of the second segment by a non-zero distance, wherein the first outer sidewall is separated from the second outer sidewall by way of a second passivation layer disposed over the molding structure and the first passivation layer; and wherein corners of the first passivation layer, the second passivation layer, the molding structure, and the first substrate meet at a first point along a first side of the first substrate and at a second point along an opposing second side of the first substrate.
 2. The package of claim 1, wherein the first passivation layer has a first upper surface over the first conductive pad and a second upper surface outside of the first conductive pad and over the first substrate, wherein the first upper surface is above the second upper surface.
 3. The package of claim 1, wherein the first passivation layer is disposed on the first conductive pad; and wherein the second passivation layer is disposed over the first passivation layer and has a bottom surface below a top of the first passivation layer, wherein the second passivation layer is arranged directly between a sidewall of the first passivation layer and a sidewall of the conductive structure.
 4. The package of claim 1, wherein the first passivation layer is disposed on the first conductive pad and on the first substrate outside of the first conductive pad; and wherein the second passivation layer continuously extends from a bottom surface contacting the molding structure to a top surface contacting a lower surface of the conductive structure, wherein the second passivation layer completely covers opposing outermost sidewalls of the first passivation layer.
 5. The package of claim 1, wherein the conductive structure continuously extends from directly over the first substrate to an outermost sidewall that is directly over the second substrate.
 6. The package of claim 5, wherein the first conductive pad and the second conductive pad comprise one or more materials that are the same material.
 7. The package of claim 1, wherein the first substrate comprises silicon and the second substrate comprises a group III-V semiconductor material.
 8. The package of claim 1, wherein the second conductive pad comprises a first metal layer, a second metal layer over the first metal layer, and the uppermost metal layer over the second metal layer; and wherein outermost sidewalls of the first metal layer, the second metal layer, and the uppermost metal layer are substantially aligned along lines.
 9. An integrated chip package, comprising: a first chip; a second chip; a molding structure laterally surrounding the first chip and the second chip; a conductive structure over the first chip and the second chip, wherein the conductive structure is coupled to the second chip by way of a conductive contact that is a multi-layer structure having an upper layer, a middle layer contacting a bottom of the upper layer, and a lower layer contacting a bottom of the middle layer, wherein the upper layer and the lower layer are a same material that is different than the middle layer; a first passivation layer having a first segment disposed over the first chip and a separate second segment disposed over the second chip; and a second passivation layer continuously extending from a bottom surface contacting the molding structure to a top surface contacting a lower surface of the conductive structure, wherein the second passivation layer completely covers opposing outermost sidewalls of the first passivation layer.
 10. The package of claim 9, wherein the same material is nickel or titanium.
 11. The package of claim 9, wherein the lower layer comprises titanium, the middle layer comprises platinum, and the upper layer comprises titanium.
 12. The package of claim 9, wherein the lower layer comprises nickel, the middle layer comprises a germanium gold alloy, and the upper layer comprises nickel.
 13. The package of claim 9, wherein the second chip comprises an optical component configured to process, receive, or transmit optical signals.
 14. The package of claim 9, further comprising: a support surface coupled to a surface of the molding structure that faces away from the conductive structure.
 15. The package of claim 9, wherein the second passivation layer comprises an optical opening defined therein to allow transmitting or receiving of optical signals.
 16. An integrated chip package, comprising: a first conductive pad disposed along an upper surface of a first chip; a second conductive pad disposed along an upper surface of a second chip; a molding structure laterally surrounding the first chip and the second chip; a conductive structure over the first chip and the second chip, the conductive structure conductively coupled to the first conductive pad and the second conductive pad; a first passivation layer arranged on the upper surface of the first chip and the upper surface of the second chip; a second passivation layer over the first passivation layer and the molding structure, wherein the second passivation layer vertically extends from below a bottom of the conductive structure to over a top of the first passivation layer, and wherein the second passivation layer is directly between a sidewall of the first passivation layer and a sidewall of the conductive structure, the sidewall of the first passivation layer and the sidewall of the conductive structure extending along imaginary lines that intersect the first conductive pad; and a third passivation layer arranged over the conductive structure, wherein a horizontal plane that is parallel to the upper surface of the first chip extends through sidewalls of the second passivation layer and the third passivation layer.
 17. The package of claim 16, wherein the first passivation layer has an outer sidewall that is vertically over the first chip and that is laterally between a sidewall of the first conductive pad facing the second conductive pad and a sidewall of the first chip facing the second chip.
 18. The package of claim 16, wherein the second passivation layer completely covers opposing outermost sidewalls of the first passivation layer and contacts the molding structure.
 19. The package of claim 16, wherein the first passivation layer and the second passivation layer directly contact an upper surface of the first conductive pad.
 20. The package of claim 16, wherein the first passivation layer comprises silicon oxide, silicon nitride, or a low-k dielectric material. 